In this post, the poster had a problem of HTML tags being stripped of their opening and closing brackets when posting in WP from WLW’.
He explains the source of the problem, and his solution:
The issue with the partially stripped HTML tags is a bug in libxml2. Specifically using anything less than PHP 5.2.9+ with libxml2 2.7.3+ is susceptible. The fix is to install a plugin into WordPress called LibXML2 Fix which you can get from your plugins menu or look here -> http://wordpress.org/extend/plugins/libxml2-fix/.
He goes on in explaining how you can find out what version of PHP and LibXML2 you are running, so you know if you’re suffering from the same problem as he is.